The focus of this protocol is the identification of genes whose genetic variation predisposes individuals to late-onset NIDDM. It involves the typing of highly polymorphic DNA markers in pairs of affected siblings and in pedigrees in order to identify and localize NIDDM-susceptibility genes. The genetic material to be studied will be obtained through GCRC protocols 6514 and 6858. In this protocol, we seek to collect genetic material and demographic, historical and physical exam data on fifty multiplex families with NIDDM.